1. Field of the Invention
This invention relates to a pulverising disc and in particular, but not exclusively, to a pulverising disc for use in pulverising mill for grinding minerals.
2. Description of the Prior Art
Pulverising mills have long been used to pulverise and grind mineral samples into a fine powder. The powder may then be used for mineral assaying or other purposes. Typically a pulverising mill comprises a metal bowl having a generally cylindrical internal side wall and a planar base. Sometimes an angled or shaped surface is also provided between the bottom of the side wall and the base of the bowl. The bowl is mounted on a vibrating table which produces vibrating motion in an essentially horizontal plane.
A mineral sample to be pulverised is placed in the bowl together with a pulverising disc and a lid clamped on the bowl. Due to the action of the vibrating table the pulverising disc is caused to move around the side wall of the bowl and as a result crush and grind the mineral sample. Typically pulverising discs are in the form of squat metal cylinders of substantially uniform thickness, although peripheral steps or bevels are often present. In some instances, a portion of the rim of the disc is machined to have a shape which corresponds to the portion of the bowl where the inner side wall meets the base. This is thought to improve the efficiency of the pulverising disc and pulverising mill. However, in practice, after a short period of use, the rim of a pulverising disc will wear to a shape corresponding the part of the bowl which it contacts. Pulverising discs of this type are disclosed in the specifications of Australian Patent No's 585751 and 570814.
A deficiency with the above prior art pulverising disc is that it adopts a simple path of motion within the bowl and has limited force generation capability which increases the likelihood of the pulverising disc stalling as well as increasing the time taken to grind a sample to a given mesh size and, indeed limits the mesh size that can be achieved.
The applicant has also found that with the movement of the pulverising disc within the bowl, a low pressure region is created between the undersurface of the disc and the bottom surface of the bowl. This creation of a low pressure region is further compounded as the material is reduced in size and can result in that low pressure region becoming sealed from the remainder of the space within the bowl which can also contribute to the pulverising disc stalling.
The present invention was developed with a view to providing a pulverising disc which can quickly and efficiently pulverise a mineral sample or other material with reduced likelihood of stalling.